On Wed, 11 Aug 2004 02:31:22 GMT, Roger Halstead
wrote:

Now that number concerns me. A piece of steel tube the length of a
normal muffler weighs almost that much. IF they claim no performance
degradation the muffler must be straight through and would hardly be
very effective, or at least hardly more effective than the stock units
which weight a *lot* more than 2#. Are you sure that wasn't Kg?

Straight through mufflers can be deceptively effective. They aren't
literally just a straight through pipe, the pipe is actually drilled
with many holes which allows the exhaust pulse to bleed off into an
outer chamber. On street cars, this outer chamber is often packed
with fiberglass, producing "Glass Packs", famed for their suppressed
rumble.

The "Swiss Muffler" is a variation on that theme. It's a long drilled
tube, or a tube rolled from stainless steel mesh, surrounded by a
solid outer tube. The space between the two is packed with stainless
steel wool. So the exhaust pulse can go straight through, but it's
energy is bled off through the holes in the inner tube.

This is very effective, but the ones I've seen are routed outside the
body. Since they parallel the wind stream, they don't greatly effect
overall drag, but they definately are there to see.

http://www.piteraq.dk/flight/muffler.html

My opinion is that anti noise regulations for GA aircraft are likely
in the future here in the USA. We know it isn't impossible to do
because the entire European continent flies with such laws.

Corky Scott